This invention relates to the microwavable food packages, and in particular, to a manner of applying microwave interactive material (metals) to the package to assist in the heating of a food product contained within the package.
Typically, in a microwavable food package having a microwave susceptor to assist in the heating of food within the package, a metal layer is applied to the package. More specifically, and as can be seen in the prior art U.S. Pat. No. 4,735,513, U.S. Pat. No. 4,553,010, U.S. Pat. No. 4,678,882, and U.S. Pat. No. 4,641,005, various types of containers for microwave usage incorporating heat susceptor material is shown. In most instances, if not all, the susceptor material, which is an electrically conductive material, such as a vapor deposition of metal onto a layer of the container, said conductive layer is integrated into the bag structure, and in most instances, is applied to an interior surface of the container, and in certain instances, either covered over by a laminar film, such as polymer film, or the metal layer is vacuum applied to the film, and then adhesively applied to the inner surface of the food container. Thus, on occasion, placing the metal in such close contact with the food product to be cooked has been undesirable, since frequently the metal layer when subjected to microwave energy has a tendency to fret, curl, or even peel, and if no interior protective layer is provided, can come into direct contact with the food product, or, may curl to the extent that it could rupture any overlying protective film, and still allow food contact with the metal film during microwaving. Such occurrences are undesirable. Because the metal layer is applied to the package containing the food, the metal layer is in close proximity to the food. When an uninterrupted or unbroken layer of metal is used as the susceptor, it alligators, or frets, or becomes crazed, as is shown in FIG. 1, when heated to high temperatures. This fretting can result after a relatively short time under microwave heating, i.e. in less than a minute. Hence, such undesirable features also can distort the relative time periods determined for heating or cooking of the particular packaged food, which may result in its undercooking, or overcooking, depending upon the extent of fretting that may have occurred. Thus, also, this condition can result in flaking of the metal from the bag, where spalling may occur at the metal edges, resulting in contamination of the food. To minimize this problem, the metal layer is often placed between two sheets of paper or the like which are held together with an adhesive compound, as shown is some prior art, as aforesaid. However, these adhesives, when heated to high temperatures in the microwave (temperatures as high as 400.degree. F. can be reached when using metal layers) can cause undesirable emissions. Further, although the layers of the bag are considered to be transparent to microwaves, they are not. Even though the microwaves do pass through the substrates, there is a loss of energy and bending of the microwaves which reduce the effectiveness of the microwave energy. The adhesives used to secure the layers of the bag together absorb microwaves and cause a loss of energy and heating to the food product and may result in over heating, brown spots and possible emissions from the adhesive in harmful amounts.